A hybrid drive system including a plurality of drive sources is, for example, employed for a traveling drive system of a vehicle, and drives the vehicle by using rotational power from at least one of an internal combustion engine and an electric motor. In such a hybrid drive system, oil for lubrication of gears in an incorporated power split mechanism, and the like, cooling of a generator-motor, or the like, is pressurized and circulated by an oil pump.
As an existing hybrid drive system including an oil pump, there is, for example, the one in which, in order to make it possible to supply oil even during EV (electric vehicle) running, an input shaft of a power split mechanism to which power from an engine is input and an output shaft of the power split mechanism that outputs power from at least one of the engine and a motor to a traveling drive system are respectively coupled to the oil pump via one-way clutches such that power is inputable, and the oil pump is driven by one of both shafts, having a higher rotation speed (see Patent Documents 1, 2).